Leukemia phenotyping. (A) Infiltration of leukemic cells in the spleen (i, ii, iii, viii), thymus (iv), liver (v, vi), and kidney (vii). (i) Erythroid leukemia. Note mitotic figures. (ii) Myeloid leukemia without maturation composed of immature blasts. (iii) Myeloid leukemia with maturation of granulocytes. (iv) T-lymphoblastic lymphoma/leukemia with starry sky cells. (v-vi) Leukemic infiltration as disseminated tumor cells in the sinusoids (v) and/or as cell nests (vi). (vii) T-lymphoblast infiltration. (viii) Myeloid leukemia associated with megakaryocytosis. Original magnifications: × 1000 (i-iv, viii); × 630 (v-vii). Hematoxylin and eosin. A light microscope (Axioplan2, Zeiss, Germany) with 63× and 100× Plan-NEOFLUAR objective lenses was used. The MRGrab (Version 1.0, Zeiss, Germany) with a digital camera (AxioCam MRc, Zeiss, Germany) was used for image processing. (B) FACS profiles of different leukemias. (C) MDR1 activity determined by rhodamine efflux in leukocytes 9 weeks after BMT and in BM cells at the day of sacrifice. Efflux-positive cells are the rhodamine-negative population. Anti-CD3 stain is shown on the y-axis. BM cells of mouse 31 showed no efflux activity after onset of leukemia, except for infiltrating T cells.